ocfs2: log the actual return value of ocfs2_file_aio_write()

in ocfs2_file_aio_write(), log_exit() could don't log the value
which is really returned. this patch fixes it.

Signed-off-by: Wengang Wang <wen.gang.wang@oracle.com>
Signed-off-by: Joel Becker <joel.becker@oracle.com>